In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.
Owing to their good ratio of rigidity and stiffness to thickness, composite materials, and in particular sandwich components, are widely used in the field of aircraft construction. Sandwich constructions are generally formed of an upper and a lower cover layer or cover ply, between which there is, for example, a honeycomb-type core structure formed of vertical cells of hexagonal cross-section, designed to increase rigidity.
Owing to their multi-functionality, cellular materials are of particular interest in component production and in the field of enhanced component properties for application in sandwich constructions for large-sized structural components, in particular in aviation. Sewing techniques, with which fibres or threads can be incorporated in rigid foam components, are used to reinforce foam-based sandwich constructions. After a resin infiltration process, the regions interspersed with fibres then help to mechanically reinforce the cellular material.
The fibres or threads (also referred to as semi-finished textiles products hereafter) used for reinforcement may be what are known as rovings, which consist of parallel fibres. They may also be threads consisting of twisted or plied fibres.
In known sewing methods, first a needle penetrates into and pierces the cellular material. At the same time, the needle thereby incorporates the thread into the cellular material. At this stage, while being inserted into the cellular material, the thread extends parallel to and substantially over the entire length of the needle. The hole size of the puncture is thus determined by the needle diameter and the thickness of the thread.
After the needle withdraws from the cellular material or textile, a hole is left behind, the diameter of which is relatively large by comparison with the diameter of the incorporated thread. This means that after resin infiltration, the hole region not filled with fibres is filled with resin, and this may increase the weight of the finished component.
DE 10 2005 024 408 A1 describes the reinforcement of cellular materials by means of a knotting method in that the needle first pierces the material (the cellular material) to be reinforced and only then, in the region of the underside of the cellular material, takes up the semi-finished textiles product (i.e. the roving or thread) and draws the same through the pierced hole upon the subsequent backward movement.
In this manner, the hole diameter can on the whole be kept relatively small.